1. Field of the Invention
The present invention relates to a detector base which is installed on a ceiling in advance and to which a detector unit is mounted.
2. Description of the Related Art
In order to prevent unauthorized removal of a detector unit of a fire detector from its base, the known detector unit and base are coupled together with a bayonet coupling, and a locking means maintains the coupled state. The locking means is designed as follows. A portion of the base block of the detector base is notched and a movable tongue is arranged in the notch in such a manner that it can be touched and swung while the fire detector unit is being mounted on the base. A recess formed at the bottom of the detector unit receives a locking projection provided on the movable tongue.
A portion of the base block of the detector base, which is thin from an aesthetic point of view, is notched and the movable tongue is arranged in the notch. It is difficult to sufficiently increase the range over which the movable tongue can be swung. Accordingly, the range over which the locking projection of the moving tongue can be swung is small, and the engagement between the locking projection of the moving tongue and the base block is accordingly weak. As a result, only a light touch on the movable tongue is sufficient to release the engagement and so, the detector unit can be easily removed from the base deliberately by mischief or the like.
Also, another type of known detector base sends information to a receiver or a transmitter when a fire detector unit is removed from its base. A pair of lines, each of which serves as both a power and a signal line and extends from a receiver or a transmitter, are connected to the detector base. When the fire detector unit is removed from the base deliberately by mischief or the like, one of the pair of lines is disconnected and thereby informs the receiver or the transmitter in the form of a disconnect signal that the first detector unit has been removed.
In this type of a detector base, one of the pair of lines is divided in half and its one end is connected to a first connecting terminal of the base while its other end is connected to a second connecting terminal of the base. When the fire detector unit is correctly mounted on the base, the first and second connecting terminals of the base are shorted by means of a jumper wire disposed within the fire detector unit. Hence, when the fire detector unit is removed from the base, the first and second connecting terminals are disconnected.
In such a detector base, it is necessary to mount the fire detector unit on the base and short the first and second connecting terminals in order to tell whether the base is correctly connected to the power and signal lines. However, if the fire detector unit is mounted on the base for that purpose, the fire detector unit might possibly be damaged during subsequent assembly work. Therefore, a jumper wire is screwed between the first and second connecting terminals. This is extremely time-consuming work in that it involves screwing a short-circuiting wire for the purpose of the inspection and unscrewing the wire after the inspection in order to mount the fire detector unit on the base.